• 한국강구조학회 논문집
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• 제21권4호
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• pp.433-442
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• 2009

본 연구는 V노치 또는 예리한 균열이 존재하는 N 다변형 단면 입체 실린더에 대한 새로운 3차원 진동 데이터를 제시한다. 본 논문에서는 수학적으로 완전한 대수삼각다항식과 V노치 선단을 따라 존재하는 3차원 응력특이도를 명확히 다루는 허용에지함수와 함께 Ritz방법이 적용된다. 응력특이도를 포함하는 다변형 입체 실린더의 정확한 고유진동수 및 모드형상을 얻기 위해서는 에지함수가 필요하다는 것이 수렴도 분석을 통하여 입증된다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.218-225
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• 2000

This paper presents intermediate results of an on-going research for identification of the modal and the stiffness parameters of a bridge based on the ambient vibration data caused by the traffic loadings. The main algorithms consist of the random decrement method incorporating band-pass filters for estimation of the free vibration signals the cross spectral density method for identification of the modal parameters and the neural networks technique for estimation of the element-level stiffness changes. An experimental study is carried out on a scaled bridge model with a composite section subjected to various moving vehicle loadings. Vertical accelerations are measured at several locations on the girder. The estimated frequencies and mode shapes are found to be well-compared with those obtained from the impact tests. The estimated stiffness changes using the neural networks are found to be very good for the case with the simulated data. However the accuracy is found to be not quite satisfactory for the case with the experimental data particularly for the small value of the stiffness changes.

• Advances in Computational Design
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• 제3권2호
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• pp.113-132
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• 2018

This paper presents the vibration and harmonic analysis of orthotropic laminated composite plate. The response of plate is determined using Finite Element Method. The eight noded shell 281 elements are used to analyze the orthotropic plates and results are obtained so that the right choice can be made in applications such as aircrafts, rockets, missiles, etc. to reduce the vibration amplitudes. Initially the model response for orthotropic plate and harmonic response for isotropic plate is verified with the available literature. The results are in good agreement with the available literature. Numerical results for the natural frequency and harmonic response amplitude are presented. Effects of boundary conditions, thickness to width ratio and number of layers on natural frequency and harmonic response of the orthographic plates are also investigated. The natural frequency, mode shape and harmonic analysis of laminated composite plate has been determined using finite element package ANSYS.

• Structural Engineering and Mechanics
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• 제82권1호
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• pp.41-53
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• 2022

We developed an accurate and simple vibration model to calculate the natural frequencies and their corresponding vibration modes for multi-span beam bridges with non-uniform cross-sections. A closed set of characteristic functions of a single-span beam was used to construct the vibration modes of the multi-span bridges, which were considered single-span beams with multiple constraints. To simplify the boundary conditions, the restraints were converted into spring constraints. Then the functional of the total energy has the same form as the penalty method. Compared to the conventional penalty method, the penalty coefficients in the proposed approach can be calculated directly, which can avoid the iteration process and convergence problem. The natural frequencies and corresponding vibration modes were obtained via the minimum total potential energy principle. By using the symmetry of the eigenfunctions or structure, the matrix size can be further reduced, which increases the computational efficiency of the proposed model. The accuracy and efficiency of the proposed approach were validated by the finite element method.

• Nuclear Engineering and Technology
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• 제47권2호
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• pp.165-175
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• 2015

The application of neutron noise analysis (NNA) to the ex-core neutron detector signal for monitoring the vibration characteristics of a reactor core support barrel (CSB) was investigated. Ex-core flux data were generated by using a nonanalog Monte Carlo neutron transport method in a simulated CSB model where the implicit capture and Russian roulette technique were utilized. First and third order beam and shell modes of CSB vibration were modeled based on parallel processing simulation. A NNA module was developed to analyze the ex-core flux data based on its time variation, normalized power spectral density, normalized cross-power spectral density, coherence, and phase differences. The data were then analyzed with a fuzzy logic module to determine the vibration characteristics. The ex-core neutron signal fluctuation was directly proportional to the CSB's vibration observed at 8Hz and15Hzin the beam mode vibration, and at 8Hz in the shell mode vibration. The coherence result between flux pairs was unity at the vibration peak frequencies. A distinct pattern of phase differences was observed for each of the vibration models. The developed fuzzy logic module demonstrated successful recognition of the vibration frequencies, modes, orders, directions, and phase differences within 0.4 ms for the beam and shell mode vibrations.

• 대한토목학회논문집
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• 제39권6호
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• pp.933-943
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• 2019

본 연구의 목적은 사회경제적 특성에 따른 장사유형 선호의 결정요인을 도출하는 것이다. 우리나라는 '장사 등에 관한 법률'에 의하여 장사유형은 매장, 봉안, 자연장으로 구분하고 있다. 본 연구는 사람들이 3가지 장사유형을 선택함에 있어 그들이 가진 어떠한 사회경제적 특성이 영향을 미치는지 실증분석하였다. 이를 위하여 2017년 사회조사 자료와 전국의 장사시설 자료를 수집하였다. 그리고 매장과 화장을 상위 계층으로 하고, 화장의 하위 계층에 봉안과 자연장이 반영된 위계 구조를 구성하여 분석용 자료를 구축하였다. 구축된 자료를 바탕으로 네스티드로짓모형을 활용한 실증분석을 실시하였다. 실증분석 결과, 장사유형의 선호에 통계적으로 유의한 영향을 미치는 사회경제적 특성은 성별, 연령, 가구주 여부, 혼인상태, 전반적인 생활에 대한 만족도, 사회경제적 지위에 대한 계층의식, 월평균 가구소득, 주택 유형, 주택 점유형태, 도시 거주 여부로 추정되었다. 네스티드로짓모형의 결과는 직접 탄력성과 교차 탄력성을 산출하여 변수별 탄력성 계수를 근거로 해석하여야 한다. 따라서 본 연구는 통계적으로 유의한 변수들의 직접 탄력성 및 교차 탄력성 계수를 산출하였다. 산출한 직접 탄력성은 통계적으로 유의한 변수가 변화할 때, 각 장사유형의 선택 확률을 해석하는데 활용하였다. 그리고 교차 탄력성은 특정 장사유형을 선택하는 경우, 나머지 장사유형을 선택하는 확률이 어떻게 변화하는지 해석하는데 활용하였다. 실증분석 결과 중 주목해야하는 점은 자연장과 관련된 사항이다. 자연장에 대한 수요를 충족하기 위한 자연장지의 공급을 활성화하고, 자연장에 대한 인식 제고를 위한 노력을 기울일 필요가 있다. 이를 통하여 국토 공간을 효율적으로 이용하여야 할 것이다.

• 한국위성정보통신학회논문지
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• 제9권1호
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• pp.57-64
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• 2014

최근 물리적 디바이스의 도움 없이 사람이 시스템과 인터랙션 할 수 있는 인간 친화적인 인간-기계 인터페이스가 많이 연구되고 있다. 이중 대표적인 것이 본 논문의 주제인 비전기반 제스처인식이다. 본 논문에서 우리는 설정된 가상세계의 객체와의 인터랙션을 위한 손 제스처들을 정의하고 이들을 인식할 수 있는 효과적인 방법론을 제안한다. 먼저, 웹캠으로 촬영된 저해상도 영상에서 사용자의 양손을 검출 및 추적하고, 손 영역을 분할하여 손 실루엣을 추출한다. 우리는 손 검출을 위해, RGB 공간에서 명암에 따라 두개의 타원형 모델을 이용하여 피부색을 모델링하였으며, 블랍매칭(blob matching) 방법을 이용하여 손 추적을 수행하였다. 우리는 플러드필(floodfill) 알고리즘을 이용해 얻은 손 실루엣의 행/열 모드 검출 및 분석을 통해 Thumb-Up, Palm, Cross 등 세 개의 손모양을 인식하였다. 그리고 인식된 손 모양과 손 움직임의 콘텍스트를 분석해서 다섯 가지 제스처를 인식할 수 있었다. 제안하는 제스처인식 방법론은 정확한 손 검출을 위해 카메라 앞에 주요 사용자가 한 명 등장한다는 가정을 하고 있으며 많은 실시간 데모를 통해 효율성 및 정확성이 입증되었다.

• 한국소음진동공학회논문집
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• 제14권10호
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• pp.1041-1047
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• 2004

This paper deals with the dynamic stability and vibration of a discontinuous cantilevered Pipe conveying fluid. The present model consists of two segments with different cross-sections. Governing equations of motion are derived by extended Hamilton's principle, and the numerical scheme using finite element method is applied to obtain the discretized equations. The critical flow velocities and stability maps of the pipe are obtained by changing ratios of second area moment of inertia and mass ratios. Finally, the vibrational modes associated with flutter are shown graphically.

• Structural Engineering and Mechanics
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• 제33권3호
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• pp.325-337
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• 2009

Structural damage detection, damage localization and severity estimation of jacket platforms, based on calculating modal strain energy is presented in this paper. In the structure, damage often causes a loss of stiffness in some elements, so modal parameters; mode shapes and natural frequencies, in the damaged structure are different from the undamaged state. Geometrical location of damage is detected by computing modal strain energy change ratio (MSECR) for each structural element, which elements with higher MSECR are suspected to be damaged. For each suspected damaged element, by computing cross-modal strain energy (CMSE), damage severity as the stiffness reduction factor -that represented the ratios between the element stiffness changes to the undamaged element stiffness- is estimated. Numerical studies are demonstrated for a three dimensional, single bay, four stories frame of the existing jacket platform, based on the synthetic data that generated from finite element model. It is observed that this method can be used for damage detection of this kind of structures.

• Wind and Structures
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• 제32권1호
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• pp.11-17
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• 2021

In recent years, there has been a tendency towards renewable energy sources considering the damages caused by non-renewable energy resources to nature and humans. One of the renewable energy sources is wind and energy is obtained with the help of wind turbines. To determine the behavior of wind turbines under earthquake loads, dynamic characteristics are required. In this study, the differential transformation method is proposed to determine the free vibration analysis of wind turbines with a variable cross-section. The wind turbine is modeled as an equivalent variable continuous flexural beam and blade weight is considered as a point mass at the top of the structures. The differential equation representing the free vibration of the wind turbine is transformed into an algebraic equation with the help of differential transformation method and the angular frequencies and the mode shapes of the wind turbine are obtained by the help of the differential transformation method. In the study, a sample taken from the literature was solved with the presented method and the suitability of the method was investigated. The same wind turbine example also modeled by finite element modelling software, ABAQUS. Results of the finite element model and differential transformation method are compared with each other and the results are in good agreement.